Typically, larger and more expensive passenger motor vehicles have used hydraulically activated and controlled power assisted steering systems. These systems relied on a continuously available hydraulic power source generated by a hydraulic pump, typically belt driven from the crankshaft pulley. When the vehicle is travelling at speed and negotiating relatively gentle turns, no or very little hydraulic force is called upon, with the full available hydraulic force only coming into effect during parking or very low speed maneuvering.
The degree of torque applied to the steering column in these systems is transferred to a hydraulic control valve system in which a torsion element allows a degree of differential rotation between that of the steering column and the pinion driving the steering rack commensurate with the torque applied. The greater the degree of twist of the torsion bar, the greater the flow of hydraulic force made available to the rack of the steering system and hence to turning of the road wheels.
While these systems have been very effective, they are considerably wasteful of energy. The pumping of hydraulic fluid must be continuous whether required or not, with attendant frictional losses from the fluid itself as well as those of the pump and its drive belt/pulley system. In addition the valve block controlling different levels of hydraulic fluid flow requires quite complex machining so that the system is both complex and expensive.
While Electrical Power Assisted Steering (EPAS) overcomes many of the above disadvantages, there remains however a precise and rather complex assembly process associated with the location of the torsion bar sensing of torque common to both hydraulic and EPAS systems. Typically the torsion bar is “locked” into its default centred position by a pinning operation. This requires the simultaneous drilling and reaming of an input shaft body and the torsion bar, followed by the insertion of a locking pin. In the automated assembly machines which carry out the centring and pinning operation, this requires additional indexing stations for drilling and reaming equipment with automated supply and insertion of pins, adding considerably to the complexity and time of the assembly process and the cost of the assembly machine.
It is an object of the present invention to address or at least ameliorate some of the above disadvantages.
Notes
    1. The term “comprising” (and grammatical variations thereof) is used in this specification in the inclusive sense of “having” or “including”, and not in the exclusive sense of “consisting only of”.    2. The above discussion of the prior art in the Background of the invention, is not an admission that any information discussed therein is citable prior art or part of the common general knowledge of persons skilled in the art in any country.